Mr Houston said he did not use the knowledge he had access to
MSPs have complained of being thwarted in efforts to get to the bottom of an alleged conflict over the extension of the First Scotrail franchise.
Hugh Henry, convener of Holyrood's Audit Committee, said he had faced incomplete answers in questioning senior civil servants.
Guy Houston quit as Transport Scotland's finance chief after concern over his shares in First Group.
It emerged he attended meetings about the £2.25bn rail franchise deal.
Mr Houston denied any wrongdoing - telling MSPs he had access to knowledge, but made no use whatsoever of the privilege.
And, venting his frustration, Mr Henry, the former Labour education minister, swore in the presence of Scotland's top civil servant, Sir John Elvidge, when he appeared before the committee.
The contract to run rail services in Scotland is the largest of its kind awarded by the Scottish Government.
Ministers' decision to extend the ScotRail franchise by three years provoked concern from opposition parties about the transparency of the process.
Mr Henry's outburst came as MSPs were grilling Sir John and human resources officer Paul Gray.
Asked for dates and times of the resignation meetings, Mr Gray responded from memory, before referring to notes in front of him.
Mr Henry said: "Drip by drip, we have got to prise from you, collectively, information that is in front of you. Frankly I regard that as unacceptable.
"You could have and should have answered that when you were asked, instead of having to wait until the argument developed."
Taking exception to the answers, Mr Henry went on: "Somewhere along the line there is a huge element, excuse the phrase, of bullshit."
Mr Gray responded: "I do apologise. It was not my intention to withhold information."
Mr Houston left his post as finance director of Transport Scotland, a government agency, after an auditor's report showed he attended meetings at which the franchise extension was discussed.
But he told the committee that bosses at the agency knew of his shareholding and he had no role in any decision-making on the deal.
"I couldn't influence any decision because I wasn't involved in any decision-making meetings," Mr Houston said.
But Lib Dem MSP Nicol Stephen, a former Scottish transport minister, claimed there were inconsistencies in the evidence.